It is often desirable to convert image data into a higher-level form. Such conversion may allow the image data to be stored more efficiently. In addition, the resultant higher-level description may be required for further processing of the image data.
Prior art methods for converting an image from a simple raster bitmap into a higher level form like a vector graphics description involve either leaving the colour data in bitmap form or converting small areas of similar colour to flat filled objects.
In the first case where a bitmap is used for the colour data of the converted image, lots of memory is used in storing the bitmap. In the second case in which small areas are converted to flat filled objects, the main problem is that rendering all the areas of flat colour is computationally expensive. An example of this is shown in FIG. 3, where shape 352 having a gradient, or blend, fill has been converted to a format in which areas of similar colour are replaced by objects with a flat colour fill. The rings of colour labelled 350 are distinct objects with no relationship in the output. Each of the rings 350 has a flat colour.
In both of the described cases, the resultant colour data may be difficult to edit using simple controls (for example, changing the start and/or end points for a linear gradient). In addition, the colour data consumes a non-trivial amount of memory.